Vegetated swales, also known as bioswales or drainage swales, are depressions in the earth designed to slow and retain stormwater and other runoff. Typically planted with dense grasses that help to catch pollutants and suspended solids, swales are an important Green Infrastructure BMP used to naturally filter and clean stormwater from small areas as well as reduce peak storm flows into local waterways.
Vegetated swales have agricultural, commercial, industrial, and urban applications. They require more room but are less expensive than stormwater pipe and gutter systems. Swales also add value as an attractive landscape feature.
They work well as part of a bioretention strategy that may also include rain gardens and stormwater detention basins.
City of Lancaster Fact Sheet (attached, PDF)